The invention relates to a solid-state trip device for an electrical circuit breaker comprising a current detection circuit delivering analog signals proportional to the current flowing through the conductors to be protected, a rectifier, measurement and power supply circuit connected to the current detection circuit and delivering between measurement terminals at least one measurement voltage, an electronic processing unit, supplied by the rectifier, measurement and power supply circuit, and to which the measurement voltage is applied, so that it delivers on an output terminal, with or without a time delay, a circuit breaker tripping order in the event of preset pick-ups being exceeded by said measurement voltage, a trip coil mounted in series with a thyristor being supplied by the rectifier, measurement and power supply circuit, the output terminal of the electronic processing circuit being connected to the thyristor gate, in such a way that the trip coil causes the circuit breaker to open when a tripping order is delivered by the electronic processing unit.
In state-of-the-art solid-state trip devices, the trip coil and thyristor are connected in series between output terminals of the power supply circuit, a tripping order being applied to the thyristor gate.
But the power supply circuit only supplies a sufficient supply voltage a certain time after the circuit breaker has closed. To give an example, a supply voltage rise time of about 35 ms can be considered as being typical. When the electronic processing unit comprises a microprocessor, the latter in addition requires a relatively long initialization time after it has been powered on, typically 30 to 50 ms, and can therefore not provide a reliable tripping order during this period.
This gives rise to a problem when breaking tests are to be carried out with solid-state trip devices. Indeed, operation of the trip device is then masked and delayed by the supply voltage rise time. Yet it is indispensable that a large short-circuit current be detected instantaneously by the circuit breaker.